Many existing and future mobile vehicular applications require high data rate broadcasting systems ensuring full continental coverage. With respect to terrestrial networks, satellite broadcasting facilitates having such continuous and trans-national coverage of a continent, including rural areas. Among existing satellite systems, Ku-band and Ka-Band capacity is widely available in Europe, North America and most of the other regions in the world and can easily handle, at a low cost, fast and high-capacity communications services for commercial, military and entertainment applications.
The application of Ku/Ka-band to mobile terminals typically requires the use of automatic tracking antennas that are able to steer the beam in azimuth, elevation and polarization to follow the satellite position while the vehicle is in motion. Moreover, the antenna should be “low-profile”, small and lightweight, thereby fulfilling the stringent aerodynamic and mass constraints encountered in the typical mounting of antennas in airborne and automotive environments.
Typical approaches for beam steering are: full mechanical scan or hybrid mechanical electronic scan. The main disadvantages of the first approach for mobile terminals is the bulkiness of the structure (size and weight of mechanical parts), the reduced reliability (mechanical moving parts are more subject to wear and tear than electronic components) and high assembling costs (less suitable for mass production). The main drawback of hybrid electronic steering is that the antenna still requires mechanical pointing; partially maintaining the drawbacks of mechanical scan antennas.
An advantageous approach is to use a full electronic steerable beam antenna, where, in azimuth and in elevation, the scan is performed electronically. This approach doesn't require mechanical rotation. These characteristics facilitate a reduction in the size and the “height” of the antenna that is important in airborne and automotive applications, and facilitate a better reliability factor than a mechanical approach due to the lack of mechanical parts.
In fully electronic phased arrays, the integration of the electronic components within the antenna aperture represents a big challenge due to the high number of components required. Often, this aspect drives the antenna design (element spacing, array lattice, element rotation) leading to a decrease of the antenna performance. The ideal configuration would consist in a radiating element integrating all the electronics in a surface area not larger than a patch antenna of the radiating element. In this way, the complete array would be designed around the radiating element only and optimized for its radiating performance.